The present invention relates to a magnetic recording and reproducing apparatus for recording and reproducing a signal which is pulse-modulated in analog manner.
When information is transmitted to the transmission line in a transmission system for transmitting information of still images, serial information is resolved every unit of image elements. Accordingly, when the signal transmitted is formed every unit of image elements, a signal process such as a transmission speed changing operation can be easily achieved. Pulse modulation is well known as a signal modulation method suitable for such transmission. Pulse modulation of analog type such as pulse phase modulation (PPM) and pulse width modulation (PWM) is better than some other pulse modulation methods to achieve narrow-band transmission. It has been reported that pulse duration modulation (PDM) can enhance pulse transmission density better than PPM because the former needs no reference pulse. A transmission method using PDM is intended to correspond in analog amount to pulse duration when an analog signal is digitized and transmitted. Therefore, fluctuations in pulse duration during transmission influences the S/N ratio of the signal directly, and it is therefore extremely important to accurately keep this pulse duration. Upon recording a signal transmitted according to the PDM method, the modulated signal may be recorded by FM modulation or the like on a recording medium. But, this requires a complicated additional circuit. Magnetic recording is an excellent method for recording a large amount of information, but when a PDM signal is recorded using the longitudinal recording method now widely employed, various problems are caused. Because the amount of peak shift is large according to the longitudinal recording method, recorded information does not correspond to reproduced information in the case where recording density dependence is present. In the case of a PDM signal, for example, pulse duration is substantially changed by recording current and density to thereby change contents of information.